America's National Security Agency and its British counterpart are among the "worst offenders" of mass surveillance, according to an open letter allegedly written by Edward Snowden. Many German public figures are now saying the NSA whistleblower should be offered asylum in their country.

"The world has learned a lot in a short amount of time about irresponsibly operated security agencies and, at times, criminal surveillance programs. Sometimes the agencies try to avoid controls," the letter reads, as translated by CNN from a version published by the German magazine Der Spiegel on Sunday.

"While the NSA and [its British counterpart] GCHQ appear to be the worst offenders – at least according to the documents that are currently public – we cannot forget that mass surveillance is a global problem and needs a global solution," the letter says.

Governments are seeking to subdue debate about the issue "with a never before seen witch hunt," charges Snowden, who was granted one-year asylum by Russia in August.

"At the beginning, some of the governments who were exposed by the revelations of mass surveillance initiated an unprecedented smear campaign. They intimidated journalists and criminalized the publication of the truth. Today we know that this was a mistake, and that such behaviour is not in the public interest. The debate they tried to stop is now taking place all over the world," Snowden said, according to The Guardian.

Snowden recently alleged that U.S. was spying on France and tapping the personal phone of German chancellor Angela Merkel. Italian Prime Minister Enrico Letta also accused Britain of intercepting secret Italian communications and passing them to the NSA.

The revelations led leaders of European Union nations to issue a common statement, warning that U.S. spying on their governments could jeopardize their joint fight against terrorism. "A lack of trust could prejudice the necessary cooperation in the field of intelligence gathering," they said in the statement on Oct. 25.

Meanwhile, the new edition of Der Spiegel carries a call by over 50 public figures in Germany for Berlin to lend more support to Snowden.

"Snowden has done the western world a great service. It is now up to us to help him," The Guardian quotes Heiner Geissler, the former general secretary of the ruling Christian Democrats, as writing in the magazine.

"The American dream is turning into a nightmare," writes public intellectual Hans Magnus Enzensberger, accusing the U.K. of having become a "U.S. colony." Enzensberger says Norway should offer asylum to Snowden.

Other public figures calling for Berlin's support to Snowden include actor Daniel Brühl, novelist Daniel Kehlmann, entrepreneur Dirk Rossmann, feminist activist Alice Schwarzer and German football league president Reinhard Rauball.

According to German newspaper Frankfurter Allgemeine Sonntagszeitung, the United States and Germany are likely to have a "no spy" agreement by early next year.

Last week, Snowden handed another letter to German parliamentarian Hans-Christian Stroebele after meeting him in Russia.

"I hope that when the difficulties of this humanitarian situation have been resolved, I will be able to cooperate in the responsible finding of fact regarding reports in the media, particularly in regard to the truth and authenticity of documents, as appropriate and in accordance with the law," the letter said.